The series was announced in March 2019 by Movistar+ and Mediapro as a teen drama full of adventure, set in the 1990s, centered around the search for missing girls.

Director Fernando González Molina recounted that the project came about after Globomedia convinced him to work with them again; he then convinced Ruth García and David Oliva to undertake the journey together.

Steven Spielberg's work and series such as V, Verano azul, and Compañeros were cited as sources of inspiration, although the project was soon compared to Stranger Things after its announcement.

Filming began in January 2020 at locations in Alicante such as Benidorm, Altea, Xàbia, Santa Pola, Calp, and L'Alfàs del Pi, with additional footage in Alhama de Aragón, the Valencia region, Madrid, and the Centro Nacional del Vidrio in La Granja (Segovia).

Filming was halted on March 12, 2020 due to the coronavirus pandemic and resumed on July 7, at a time when safety protocols were still unclear, according to production manager Laura Fernández Espeso.

Filming for season 2 began on May 17, 2021 in Begur (Girona), once again under the direction of Fernando González Molina.

The music was composed by Lucas Vidal, supplemented by songs from OBK and Mecano, while the main theme was performed by Ana Torroja.

Just one day after the release of the first season, on June 5, 2021, it was confirmed that the series was renewed for a second season, with filming beginning in July of that same year.

The series was compared by multiple critics to the American series Stranger Things because of its plot and aesthetics, and the first episode was praised as one of the best pilots of recent Spanish fiction.